1. Technical Field
The present invention relates to a technique for preventing the deterioration of display quality appearing in a column direction.
2. Related Art
In recent years, projectors in which, first, a small image is formed by an electro-optical panel using, for example, liquid crystal and then the small image is enlarged by an optical system to be projected onto a screen have come into widespread use. The projector does not have a function of forming an image, but is supplied with image data (or image signals) from a host device, such as a personal computer or television tuner. The image data designates the gray-scale levels (brightness) of pixels, and is supplied by vertically and horizontally scanning the pixels arranged in a matrix. Therefore, it is preferable to drive the electro-optical panel used for the projector in this manner. Thus, generally, the electro-optical panel used for the projector is driven in a so-called dot-sequential method in which scanning lines are sequentially selected, data lines are sequentially selected one by one in a period in which one scanning line is selected (one horizontal scanning period), the image data is converted into image signals suitable for driving the liquid crystal, and then the converted signals are supplied to the selected data line.
Meanwhile, in recent years, there has been proposed a technique of improving the resolution of a display image. A high-resolution display image can be achieved by increasing the number of scanning lines and the number of data lines. However, in this case, the larger the number of scanning lines is, the shorter one horizontal scanning period becomes. In addition, in the dot-sequential method, the larger the number of data lines is, the shorter the period where the data lines are selected is. Therefore, in the dot-sequential method, it is difficult to secure a sufficient time to supply the image signals to the data lines as the resolution of displayed images improves, which results in insufficient writing of the image signals onto the pixels.
Therefore, in order to solve the problem of insufficient writing, there has been suggested a phase-expansion driving method (see Japanese Unexamined Patent Application Publication No. 2000-112437). In the phase-expansion driving method, blocks each composed of a predetermined number of data lines, for example, six data lines, are simultaneously selected in one horizontal scanning period, and image signals to be supplied to pixels corresponding to the selected scanning line and the selected data lines are expanded in the time axis direction and are then supplied to the six selected data lines, respectively. In the phase-expansion driving method, it is possible to secure a time when the image signals are supplied to the data lines that is six times longer than that in the dot-sequential method. Thus, the phase-expansion driving method is suitable for improving the resolution of a displayed image.
However, when the size of a panel increases, manufacturing costs thereof also increase. Therefore, it is preferable to increase the number of scanning lines and the number of data lines per unit length in order to improve the resolution. In particular, when the number of data lines per unit length increases, an arrangement pitch between the data lines is narrowed, which causes capacitive coupling to easily occur between the data lines. As a result, a voltage variation of a data line has an effect on adjacent data lines, which leads to the deterioration of the display quality.